Electromechanical transducing arrangement



1956 R. T. CHRISTENSEN ,7

ELECTROMECHANICAL TRANSDUCING ARRANGEMENT Filed May 15, 1952 INVENTOR. RAYMON D T. CHRISTENSEN HIS ATTORNEY.

United States Patent '0 ELECTROMECHANICAL TRAN SDUCING ARRANGEMENT Raymond T. Christensen, Oak Park, Ill., assignor to Zenith Radio Corporation, a corporation of Illinois Application May-15, 1952, Serial No. 287,939

Claims. (Cl. 179-110) This invention pertains to an improved electromechanical transducer particularly suited for translating signals in .the audible range of frequencies into electrical potentials suitable for amplification. The invention is especially valuable in a wearable microphone unit in which connection it will be described.

A microphone unit to be worn in close association with a persons clothing should possess a number of qualities, some of which are difficult to obtain in combination with the others. Specifically, the microphone should be compact, inexpensive, and eificient in operation; furthermore, it should be insensitive to vibrations caused by shifting of the wearers clothing or by rubbing of other articles against the clothing. Additionally, the microphone unit in many instances should preferably exhibit at least some degree of directional discrimination in picking up sounds in the audible frequencies.

One of the more successful wearable microphones of the prior art comprises a piezo-electric element of the bender type, suspended from a mounting base at two points near the extremities of the element. A soundsensitive diaphragm is mechanically connected to a central portion of the piezo-electric transducer and sound vibrations, impinging upon the diaphragm, stress the transducer and cause it to bend, creating an electrical potential between theterminals of the transducer which is proportional to the amplitude and frequency of the sound waves. While arrangements of this type may be highly compact and exhibit a relatively high degree of etficiency in operation, they are vessentially omni-directional and also tend to pick up extraneous undesirable vibrations caused by shifting of the wearers clothing.

It is an object of this invention, therefore, to provide an improved electromechanical transducer which is extremely compact and relatively highly efiicient and which also discriminates against sounds from at least some directions.

It is a further object of this invention to provide an improved electromechanical transducer for a wearable microphone which is-relatively insensitive to mechanical vibrations occasioned by shifting of the wearers clothing or the rubbing of other articles against the clothing.

It is a specific object of the invention to provide an improved transducer which is both simple and inexpensive to construct.

An electromechanical transducer arrangement, in accordance with the invention, comprises a support mem her and a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of the bending stress, and pivotally supported about a reference axis of the transducer by the support member. A plurality of independent loading devices are individually mechanically coupled to the transducer at loadingpoints spaced from its reference axis and from each other in order to impart a bending moment to the transducer in response to balanced concurrent actuation of the loading devices,

and to pivot thetransducer about the reference axis in response to unbalancedconcurrent actuation of the load ing devices. Means are also provided for deriving a potential from the transducer indicative of its condition of stress.

The features of the present invention which are believed to be novel are set forth with particularity .in the appended claims. The invention, together with further objectsand advantages thereof, may best be understood, however, .by reference to the following description taken in connection with the accompanying drawings in the several figures of which like reference numerals indicate like elements and in which:

Figure 1 is an-exploded isometric view of a wearable microphone employing .one embodiment of the electromechanical transducingarrangement of the invention;

Figures 2A and 2B are partially schematic sectional views of theapparatus of Figure .1 after assembly; and

Figure 3 is an exploded isometric view of va microphone unit including another embodiment of the .inventron.

The wearable microphone unit illustrated in the exploded view of Figure 1 includes a case 10, here shown as a five-sided box-like structure. A support member 11 is centrallylocated'within case 10 and may be forrned integrally with the case. Support member 11 comprises a mounting base for a piezo-electric transducer 12 when the unit is assembled the transducer is mechanically supported by member 11 for pivotal movement about its reference axis 13, which in this instance comprises a central transverse axis of. the transducer. Transducer 12 may be manufactured from any suitable material having piezo-electric properties which create apotential .difierential Within the. material when it is subjected to a bending stress and may be.of the ceramic type disclosed in Patout No. 2,540,412 issued to Robert Adler and assigned to the same assignee as this application.

A pair of conductive elements 14 and 15-are electrically connected to transducer 12 and are adapted for connection to an electrical amplifying system of any suitable standard type such as a hearing-aid amplifier unit or a public address system audio amplifier; the connecting leads and amplifier have not'been shown. A pair of mechanical links 16 and 17 are fixed to transducer .12 in position to provide a mechanical connection between the transducer and apair. of suitable loading devices 22 and :23, as will be more completely described hereinafter. A frame member 18, which is adapted to engage the side walls of case it), includes a supporting rim 2i) and a supporting cross piece 21 comprising a mounting ,base for loading devices Hand 23. A cover 24 is provided for the microphone unit and includes a plurality of openings 25 for admission of sound vibrations to the loading devices.

The assembled position and inter-relationship ofthe component parts numerated in connection with Figure 1 are more clearly illustrated in Figures 2A and 2B. As indicated in Figure 2A, central reference axis 13 of transducer 12 is engaged by support member 11; the mechanical connection between these members may be effectively maintained by use of an elastic-bonding agent such as that known commercially as Minnesota Mining Cement EC833 or other suitable cement with similar properties. This type of bonding. agent is employed to permit attaching transducer 12 to member '11 without substantially restricting pivotal movement of the transducer aboutzthe support. It is essential that the transducer be freely movable about member 11, ,as will be explained more fullyhereinafter. Loading devices 22, 23, which are preferably sound-sensitive diaphragms t'ormed from 0.1"v l minum foil o mila ma e i l. are bon e 16 and r spe t ve y; any su tab F r n or h der may be employed to effect this mechanical connection. The conductive elements 14 and of Figlre l are schematically shown in Figure 2A as electrical leads 14 d x, a y The operation of the ,inventionwill be most clearly understood when considered in connection with Figures 2A and 2B. In the former, the solid outline indicates the condition of the apparatus when loading devices 22, 23 are at rest, that is to say, when there are no sound vibrations impinging upon the diaphragms. For this condition, transducer 12 is in its normal unstressed state and no potential appears between leads 14' and 15'. Consider now, that an unbalanced mechanical vibration impinges upon diaphragm 23 but leaves loading device 22 substantially unaffected. For the sake of simplicity, the unbalanced vibrational force will be considered as a simple mechanical bias urging diaphragm 23 in the direction indicated by arrow A. Under these conditions, diaphragm 23 and transducer 12 are urged along the direction of arrow A and transducer 12 pivots at reference axis 13 about the member 11. The transducer is thus forced into the position 12', indicated in dotted outline, but is not appreciably deformed, since there is no restricting force operating on diaphragm 22 to hinder the pivotal movement. The piezo-electric properties of transducer 12 require that a bending stress be applied in order to create a potential difference between leads 14' and 15', and it Will therefore be apparent that the unbalanced force applied does not change the electrical conditions of the transducer and provides no signal potential on the leads. Figure 2B is identical with Figure 2A with the single exception that in this View two concurrent forces are applied to leading devices 22, 23 as indicated by arrows A and A. Under these conditions, transducer 12 is subjected to a balanced bending force which stresses it into the configuration indicated by the dotted outline 12". This alteration in the physical configuration of the transducer creates a potential differential between electrical leads 14' and 15 which is proportional to the amplitude of the common force or balanced forces applied. It will be understood that if the simple forces described in connection with Figures 2A and 2B are replaced by the complex wave forms of audible sound vibrations there will still be no signal produced under the unbalanced conditions of Figure 2A, Whereas when balanced waves are applied in the manner of Figure 2B an electrical signal will be impressed on leads 14' and 15' which is proportional to the amplitude and frequency of sound vibrations. When the structure of the invention is employed in a wearable microphone unit such as that illustrated in Figure 1, it substantially obviates the effects of vibrations which impinge on one of the diaphragms but not on the other. This action effectively eliminates much of the clothing noise caused by shifting of the wearers clothing or rubbing of some article against the clothing, since ordinarily vibrations of this type will affect only one of the two loading devices. The arrangement also provides some discrimination as to the direction of the sound by which his actuated because vibrations impinging upon the microphone from a considerable angle with respect to the axes of the loading devices tend to affect one of the diaphragms more strongly than the other.

The microphone unit illustrated in the exploded view of Figure 3 includes a case 26 which is basically similar to case 10 of Figure 1 but which is triangular rather than rectangular in shape. Case 26 includes a support member 27 which is preferably substantially conical (as shown) or hemispherical in configuration. The microphone includes a piezo-electric transducer 28 comprising a central reference portion 30 disposed about a reference axis and three extension arms 31, 32 and 33. This type of construction is adopted to retain maximum flexibility in the piezo-electric transducer; however, a transducer of simple triangular configuration may be employed. Suitable con- .duc tive elements 34 and 35 are connected to transducer 28 to permit derivation of an electrical potential therefrom and three mechanical links 36, 37 and 38 are fixed to arms 31, 32 and 33 respectively to provide for the mechanical connection of three loading devices 40, 41 and 42 thereto. Loading devices 40, 41 and 42, here shown as conical vibratile diaphragms, are supported by a frame member 43 and enclosed by a cover 44 when the microphone unit is assembled. A plurality of sound emitting openings 45 are formed in cover 44 to permit transmission of sound vibrations to the loading devices.

The operation of the apparatus illustrated in Figure 3 will be generally apparent from the foregoing description of the functioning of the apparatus of Figures 2A and 2B. Briefly, this embodiment requires that any vibrations impinge upon all three of the load devices 41, 42 and 43 in order to produce a signal across leads 34, 35, since vibrations which affect only one or two of the diaphragms result only in pivotal movement of the transducer 28 about support member 27 without producing a bending stress in the transducer and therefore without altering its electrical condition. The directional and noise-suppressing characteristics are therefore basically and essentially similar in nature to those of the apparatus of Figure 1. In addition, this embodiment of the invention is normally more efficient in avoiding the deleterious effects of clothing noise vibrations in that suppression thereof is unlimited with respect to direction, there being no clear axis between the loading devices employed.

The invention, as described above, comprises a structure which is relatively simple in form and inexpensive to construct; the transducer arrangement is extremely compact and highly efiicient. It possesses all the advantages of the prior art arrangement previously discussed and in addition is relatively insensitive to undesirable mechanical vibrations which affect only one of the plurality of loading elements. When employed in a wearable microphone, the invention eliminates a substantial portion of the clothing noises and, in addition, exercises some degree of directional discrimination with respect to the sound to which it is sensitive. It has further been discovered that there is a more desirable frequency response and attendant increased intelligibility with such a microphone.

The description of the operation of the invention included herein is based upon the results of empirical observations reported by hearing aid users and is intended to convey a possible explanation of the effects derived; it is not to be considered as an exhaustive theoretical explanation of the results derived. While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. An electromechanical transducing arrangement comprising: a support member; a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of said bending stress, pivotally supported about a reference axis by said support member; a plurality of independent diaphragms individually mechanically coupled to said transducer at loading points spaced from said reference axis and from each other for imparting a bending moment to said transducer in response to balanced concurrent actuation of said diaphragms and for pivoting said transducer about said reference axis in response to unbalanced concurrent actuation of said devices; and means for deriving a potential from said transducer indicative of its condition of stress.

2. An electromechanical transducing arrangement comprising: a support member; a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of said bending stress, pivotally supported about a central reference axis by said support member and provided with a plurality of outwardly extending arms terminating in loading points substantially symmetrically positioned with respect to said axis; a plurality of independent loading devices individually mechanically coupled to said transducer at an assigned one of said loading points for imparting a bending moment to said transducer in response to balanced concurrent actuation of said devices and for pivoting said transducer about said reference axis in response to unbalanced concurrent actuation of said devices; and means for deriving a potential from said transducer indicative of its condition of stress.

3. An electromechanical transducing arrangement comprising: a support member; a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of said bending stress, pivotally supported about a reference axis by said support member; a plurality of independent audio-frequency-sensitive diaphragms individually mechanically coupled to said transducer at loading points substantially symmetrically positioned with respect to said reference axis moment to said transducer in response to balanced concurrent actuation of said devices and for pivoting said transducer about said reference axis in response to unbalanced concurrent actuation of said diaphragms; and means for deriving a potential from said transducer indicative of its condition of stress.

4. An electromechanical transducing arrangement comprising: a support member; a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of said bending stress, pivotally supported about a reference axis by said support member; a pair of inde- 6 pendent loading devices individually mechanically coupled to said transducer at loading points on opposite sides of said reference axis for imparting a bending moment to said transducer in response to balanced concurrent actuation of said devices and for pivoting said transducer about said reference axis in response to unbalanced concurrent actuation of said devices; and means for deriving a potential from said transducer indicative of its condition of stress.

5. An electromechanical transducing arrangement comprising: a support member; a piezo-electric transducer, responsive to an induced bending stress to develop an electrical output signal indicative of variations in the magnitude of said bending stress, pivotally supported about a central reference axis by said support member; a pair of independent diaphragms individually mechanically coupled to said transducer at loading points on opposite sides of and substantially equidistant from said reference axis for imparting a bending moment to said transducer in response to balanced concurrent actuation of said devices and for pivoting said transducer about said reference axis in response to unbalanced concurrent actuation of said diaphragms; and means for deriving a potential from' said transducer indicative of its condition of stress.

References Cited in the file of this patent UNITED STATES PATENTS 1,688,744 Nicolson Oct. 23, 1928 1,741,533 Nicolson Dec. 31, 1929 1,766,044 Nicolson June 24, 1930 2,184,247 Baumzweiger Dec. 19, 1939 2,198,424 Baumzweiger Apr. 23, 1940 2,270,167 Meissner et a1 June 13, 1942 2,444,620 Williams et al. July 6, 1948 

